package com.feiyangedu.sample;

import java.nio.charset.StandardCharsets;
import java.security.GeneralSecurityException;
import java.security.SecureRandom;
import java.util.Base64;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

public class AES_CBC_Cipher {

	static final String CIPHER_NAME = "AES/CBC/PKCS5Padding";

	// 加密:
	public static byte[] encrypt(byte[] key, byte[] input) throws GeneralSecurityException {
		Cipher cipher = Cipher.getInstance(CIPHER_NAME);
		SecretKeySpec keySpec = new SecretKeySpec(key, "AES");
		// CBC模式需要生成一个16 bytes的initialization vector:
		SecureRandom sr = SecureRandom.getInstanceStrong();
		byte[] iv = sr.generateSeed(16);
		IvParameterSpec ivps = new IvParameterSpec(iv);
		cipher.init(Cipher.ENCRYPT_MODE, keySpec, ivps);
		byte[] data = cipher.doFinal(input);
		// IV不需要保密，把IV和密文一起返回:
		return join(iv, data);
	}

	// 解密:
	public static byte[] decrypt(byte[] key, byte[] input) throws GeneralSecurityException {
		// 把input分割成IV和密文:
		byte[] iv = new byte[16];
		byte[] data = new byte[input.length - 16];
		System.arraycopy(input, 0, iv, 0, 16);
		System.arraycopy(input, 16, data, 0, data.length);
		// 解密:
		Cipher cipher = Cipher.getInstance(CIPHER_NAME);
		SecretKeySpec keySpec = new SecretKeySpec(key, "AES");
		IvParameterSpec ivps = new IvParameterSpec(iv);
		cipher.init(Cipher.DECRYPT_MODE, keySpec, ivps);
		return cipher.doFinal(data);
	}

	public static byte[] join(byte[] bs1, byte[] bs2) {
		byte[] r = new byte[bs1.length + bs2.length];
		System.arraycopy(bs1, 0, r, 0, bs1.length);
		System.arraycopy(bs2, 0, r, bs1.length, bs2.length);
		return r;
	}

	public static void main(String[] args) throws Exception {
		// 原文:
		String message = "Hello, world! encrypted using AES!";
		System.out.println("Message: " + message);
		// 128位密钥 = 16 bytes Key:
		byte[] key = "1234567890abcdef".getBytes("UTF-8");
		// 加密:
		byte[] data = message.getBytes(StandardCharsets.UTF_8);
		byte[] encrypted = encrypt(key, data);
		System.out.println("Encrypted data: " + Base64.getEncoder().encodeToString(encrypted));
		// 解密:
		byte[] decrypted = decrypt(key, encrypted);
		System.out.println("Decrypted data: " + new String(decrypted, "UTF-8"));
	}

}
